1. Field of the Invention
The present invention relates to a plasma display panel and a method of driving such a plasma display panel, and more particularly to a three-electrode AC-discharge color plasma display panel and a method of driving such a three-electrode AC-discharge color plasma display panel.
2. Description of the Prior Art
Plasma display panels for use as wide-area flat display units for personal computers, work stations, and wall-hanging television sets are roughly classified according to operating principles into DC-discharge plasma display panels in which electrodes are exposed to a discharge gas and discharge only while a voltage is being applied to the electrodes, and AC-discharge plasma display panels in which electrodes are covered with a dielectric layer and discharge while they are not exposed to a discharge gas. In the AC-discharge plasma display panels, discharge cells themselves have a memory function imparted by the charge storage action of the dielectric layer.
One general three-electrode AC-discharge plasma display panel (hereinafter also referred to as an "AC-PDP" or "PDP") will be described below with reference to FIG. 1 which shows the PDP in cross section.
As shown in FIG. 1, the PDP comprises a face plate 10 made of glass, back plate 11 made of glass, scan electrodes 12 and common electrodes 13 which are disposed parallel to each other on face plate 10, dielectric layer 15a covering scan electrodes 12 and common electrodes 13, protective layer 16 made of MgO or the like for protecting dielectric layer 15a from discharges, data electrodes 19 disposed on back plate 11 perpendicularly to scan electrodes 12 and common electrodes 13, dielectric layer 15b covering data electrodes 19, phosphor 18 coated on dielectric layer 15b for converting an ultraviolet radiation generated upon discharges into visible light for color display, and partitions 17 extending between phosphor 18 and protective layer 16 to define a discharge space therebetween and dividing the discharge space into unit discharge spaces 20. A mixture gas of He, Ne, Xe, etc. is sealed as a discharge gas in the discharge space. The areas of unit discharge spaces 20 are colored by phosphor 12 with red (R), green (G), and blue (B) to make it possible for the PDP to display color images.
A writing discharge, which determines whether or not each of the unit discharge spaces 20 emits light, is a discharge (called "opposing discharge") across an opposing discharge gap between dielectric layer 15a and dielectric layer 15b along the height of partitions 17 (with the thicknesses of protective layer 16 and phosphor 18 being ignored), and a sustaining discharge, which determines a quantity of light to be emitted, is a discharge (called "surface discharge") across a surface discharge gap in the unit discharge space.
FIG. 2 shows in plan a planar matrix of the three types of electrodes, i.e., scan electrodes 12, common electrodes 13, and data electrodes 19, and the unit discharge spaces of the color PDP shown in FIG. 1. FIG. 2 also illustrates a driver system for those electrodes.
As shown in FIG. 2, frames surrounding the reference characters R, G, B represent the respective unit discharge spaces that are surrounded by the partitions. The reference characters R, G, B indicate colors of emissions that are caused by discharges in the unit discharge spaces. Three adjacent ones of the unit discharge spaces R, G, B display a desired color by combining the three colors which are generated thereby. Such three adjacent unit discharge spaces R, G, B are collectively referred to as a "picture element", and each of the unit discharge spaces as a "pixel". Therefore, FIG. 2 shows a matrix of these pixels on the display screen of the color PDP, and the scanning, common, and data electrodes for applying scanning, data, and sustaining pulses to the pixels.
Scan electrodes 12 and common electrodes 13 extend parallel to each other horizontally across the display screen, and data electrodes 19 extend parallel to each other vertically in perpendicular relation to scan electrodes 12 and common electrodes 13. Three adjacent pixels R, G, B, which jointly make up a picture element, are arranged along each of scan electrodes 12. Scan electrodes 12 are separately connected to scan driver 4, and data electrodes 19 are separately connected to data driver 5. Common electrodes 13 are commonly connected to sustain driver 1 (sustain driver for common electrodes). Second sustain driver 2 (sustain driver for scan electrodes) is connected through scan driver 4 to scan electrodes 12. Sustain driver 1 and second sustain driver 2 are connected to control driver 3 which produces a control signal for determining at least the oscillation frequency of sustaining pulses.
When the pixels or the unit discharge spaces are scanned by scan pulses applied from the scan electrodes 12 and data pulses are applied from data electrodes 19 in synchronism with the scan pulses, writing discharges, which are opposing discharges, are generated in the unit discharge spaces depending on display information that are given by the data pulses. Then a potential difference due to a wall charge (described later on) created by the writing discharges is added to the voltage of sustaining pulses thereby causing a sustaining discharge, which is a surface discharge, between scan electrodes 12 and common electrodes 13.
A process of driving the PDP will be described below with reference to FIG. 3 which shows the waveform and time sequence of drive voltages applied to the electrodes in one subfield. First, erase pulses 21 are applied to scan electrodes 12 to turn off those pixels which have emitted light in a preceding subfield, thereby turning off all the pixels. Then, priming discharge pulse 22 is applied to common electrodes 13 to discharge all the pixels to emit light compulsorily, after which priming erase pulses 23 are applied to scan electrodes 12 to turn off the priming discharges of all the pixels. The priming discharges make subsequent writing discharges easy.
After the priming discharges are turned off, scan pulses 24 are applied in a time-division fashion to the respective scan electrodes 12, and, in synchronism with scan pulses 24, data pulses 27 are applied to data electrodes 19 depending on whether there is lighting data of each pixel or not. Writing discharges occur in those pixels where data pulses 27 are applied when scan pulses 24 are applied. However, no writing discharges occur in those pixels where no data pulses 27 are applied when scan pulses 24 are applied. Diagonal lines at the data pulses 27 indicate that the presence or absence of data pulses 27 is determined depending on whether there is lighting data or not. It is assumed that scan pulses 24 are of negative polarity, data pulses 27 are of positive polarity, and sustaining pulses 25, 26 are of negative polarity.
In pixels where writing discharges occur, a positive charge called a wall charge is stored in dielectric layer 15a on scan electrode 12, and a first sustaining discharge is generated due to the sum of a positive potential owing to the wall charge and a voltage of first sustaining pulse 25 applied to common electrode 13. If the voltages of sustaining pulses 25 and 26 are adjusted in advance such that no discharges will be generated by any of the voltages of the sustaining pulses, the first and the subsequent sustaining discharges can not be generated in pixels where no writing discharges occur, since there is no potential due to a wall charge before first sustaining pulse 25 is applied. When the first sustaining discharge is generated, positive wall charges are stored in dielectric layer 15a on common electrodes 13, and negative wall charges are stored in dielectric layer 15a on scan electrodes 12. The potential difference due to the wall charges is added to sustaining pulses 26 applied to scan electrodes 12, and a second sustaining discharge occurs. A potential difference due to the wall charges produced by an xth sustaining discharge and a voltage of (x+1)th sustaining pulse are added to generate an (x+1)th sustaining discharge. After writing discharges are generated, sustaining pulses 25, 26 are applied alternately to scan electrodes 12 and common electrodes 13 to maintain sustaining discharges. The quantity of emitted light is determined by the number of times that sustaining discharges are maintained.
FIG. 4(a) shows a picture element which is a collection of three pixels R, G, B arranged along a scan electrode in the PDP shown in FIG. 2, and FIG. 4(b) shows scanning pulse 24 and data pulses 27 which are applied to generate writing discharges in pixels R, B, except pixel G. A process of selective display in each of the pixels will be described below with reference to FIGS. 4(a) and 4(b). Pixel G in FIG. 4(a) is shown hatched to indicate that pixel G is not emitting light.
Since scan electrode 12 extends across three pixels R, G, B that jointly make up one picture element, scan pulse 24 is applied simultaneously to these three pixels R, G, B. When scan pulse 24 is applied, data pulses 27 are applied respectively to data electrodes 19a, 19c of pixels R, B, and no data pulse is applied to data electrode 19b of pixel G. Writing discharges occur and shift to sustaining discharges in pixels R, B, and a writing discharge does not occur and does not shift to a sustaining discharge in pixel G. Therefore, whether three pixels R, G, B that jointly make up one picture element are to be energized to emit light or not is selected during one scan pulse. Stated otherwise, a scan pulse applied to the pixels that emit different colors is supplied from the same scan electrode.
Similarly, the respective sustaining pulses from scan electrodes 12 and common electrode 13 are applied simultaneously to pixels that emit different colors.
As explained above, in the matrix of pixels and electrodes shown in FIG. 2, because a scan electrode and a common electrode are shared by three pixels that jointly make up a picture element, i.e., three unit discharge spaces, the same sustaining pulse is applied to the pixels that emit different colors.
When the number of sustaining pulses for determining the quantity of emitted light is the same among pixels R, G, B, if the quantity of light emitted from pixel B is smaller than the quantity of light emitted from pixels R, G due to the characteristics of their phosphors, then a white image displayed by these pixels tends to be yellowish. Such a drawback may be avoided by using a correction circuit for increasing the level of a display luminance signal supplied to the pixel B. However, the correction circuit would make invalid a low-bit display luminance signal supplied to pixel B, reducing the number of gray levels that can be represented by pixel B. Furthermore, after the correction circuit is adjusted, it would be difficult to change the corrective quantity thereof, i.e., to adjust the color balance.
Moreover, since the same scan pulse is applied to the pixels that emit different colors, it is difficult to cause appropriate writing discharges all over the display screen. Pixels R, G, B have different conditions to be met for causing appropriate writing discharges because of different charging characteristics of the phosphors of pixels R, G, B. For example, when it is more difficult for pixels G to cause appropriate writing discharges and it is easier for pixels B to cause appropriate writing discharges, if scanning pulses to be applied to a scan electrode are established with their voltage and width selected for pixels G to be able to cause appropriate writing discharges, then pixels B on the same scan electrode may possibly cause writing discharges in error.